The specific aim of this study is to test the hypothesis that physiological hyperinsulinemia stimulates serum leptin release in normal human subjects. There is presently very little information relative to the mechanisms which control leptin release in humans. A rise in serum leptin could be the consquence of either hyperglycemia or hyperinsulinemia or both. In order to distinguish between these possibilities, we plan to raise insulin levels while maintaining euglycemia for 72 hr in normal and obese controls, and in obese NIDDM patients.